After printing on plastic film or transparent paper, there may be a dry illusion on the printed surface. However, during the storage period after printing rolls or making bags, the phenomenon of backside sticking may occur. In severe cases, the prints cannot be torn apart, and there may be ink layer transfer, leading to product rejection. This phenomenon is more likely to occur in high-temperature seasons, but high temperature is not the only cause of back sticking. Concave sticking is closely related to a series of factors such as plastic, ink, solvent, air volume, light, and speed.
Incomplete Evaporation of Solvents:
The evaporation speed of solvents is a crucial factor determining the drying of the ink layer and affecting printing quality. Slow solvent evaporation leads to good plate reproducibility and beautiful color in prints but is prone to sticking. Conversely, it can cause issues like whitening of prints. Therefore, choosing solvents with an appropriate evaporation rate is critical in gravure printing on plastic film.
In continuous multi-color printing, solvents must completely evaporate during the time the film travels between two printing stations. Otherwise, in the next station, the film may stick to the roller.
After printing on the film, if organic solvents in the ink do not completely evaporate in the drying system, and the film roll still has residual heat, it provides conditions for the continued evaporation of solvents, leading to adhesion.
In hot and humid seasons, excessive tension or compression during the winding of printed films.
Countermeasures:
Adjust the evaporation speed of solvents based on environmental conditions. If the ink layer dries too quickly, add slow-evaporating solvents; otherwise, add fast-evaporating solvents.
Films should be loosely wound and placed in wire baskets after printing to allow continued ventilation and drying of the ink layer. After curing, proceed with slitting and bag making.
Poor Ink Properties:
Some connecting agents in certain plastic gravure inks have a low melting point. In high-temperature and high-humidity conditions, they are prone to sticking.
Countermeasures:
Install air conditioners in the workshop to control the room temperature between 18°C and 21°C and the relative humidity below 65% when possible.
Replace the ink with better properties.
Poor Suitability of Film for Printing:
Films made from non-packaging resins or with insufficient slip agents in the resin can lead to poor adhesion.
Countermeasures:
Replace the plastic film.
Static Electricity:
Static electricity in plastic film products can cause the films to stick together.
Countermeasures:
Add anti-static agents to the plastic.